Electronic device



May 21, 1940. c $M|T|-| 2,201,819

ELECTRONIC DEVICE Original Filed March 5, 1.925 Z-Sheets-Sheet 1 I 21, 1940- c. 6. SMITH I 2,

ELECTRONIC DEVICE Originai Filed Mar h 5,1925 2 Sheets-Sheet 2,

charm; asmak;

3 I IIIIIIIIIIIIIIIIIIIIIIII Patented May 21, 1940 UNITED STATES PATENT orrlcs ELECTRONIC DEVICE Delaware Application March 5, 1925, Serial No. 13,145- Renewed August 23, 1933 29 Claim.

This invention relates to electronic space discharge devices having a cathode and an anode, for use as unidirectionaldischarge devices or rectiflers, etc.

Particular objects of the invention are to be able to pass current at a low potential difference between cathode and anode, to avoid excessive heating of the electrodes and associated parts by the cathode-anode current, to make "the current substantially independent of ionization by the cathode-anode current throughout the range of current values, to produce ample electronic emission from the cathode, to direct the electronic discharge to the anode with minimum resistance, and to prevent electronic conduction from anode to cathode in response to reverse potential as in rectifying, and in some cases to eliminate the space charge in the region of the anode.

In one aspect the invention comprises 'a low pressure tube, of the order of .01 mm. of mercury (10 microns), e. g., containing a cathode having a substantial pressure maintained in the region of its discharge surface for the purpose of obtaining ample electronic emission. The gas which fills the tube is preferably inert with respect to the electrodes. A diiference of pressure may be maintained by an obstruction between the electron source and the electron-receiving area, the obstruction having an opening therethrough for the passage of electrons and the opening being so restricted that a difference of pressure (or state of ionization) may be maintained on opposite sides of the obstruction. As will appear hereinafter, the obstruction is preferably formed as a part of the cathode. Under constant conditions of operation, the pressure within the cathode is preferably static in contradistinction to pressure resulting from continuous flow into the cathode and restricted flow out of the cathode. This is conveniently effected by trapping the gas within the hollow cathode with an electric field, the field being so related to the electron discharge opening in the cathode that gas molecules or ions, or both, may wander into the cathode but are restrained from escaping, at least until the pressure Within the cathode builds up to a relatively high value. This electric pumping action is preferably produced, at least in part, by the thermal ionization of the molecules in the region of the opening in the cathode with heat derived from the cathode or other suitable charge. The said field may be produced in many ways, as by one or more auxiliary electrodes, one or more anodes positioned close to the mouth of the cathode, etc., but it is preferably effected by making the cathode mouth elongated and producing a potential gradient therealong, the outer end of the mouth being positive relative to the inner end. This pumping and trapping action is most effective when the diameter of the cathode opening is substantially within the limits of the mean free path of the molecules of gas outside the cathode; and owing to the low pressure outside the cathode, this mean free path is long, thereby permitting a fairly large cathode opening.

In another aspect the invention consists in heating a hollow cathode independently of the flow of discharge current between cathode and anode, thereby to ionize the gas within the oathode independently of the cathode-anode current (that is, thermally instead of or in additionto collision) and to augment the emission and conduction of electrons from the interior of the cathode. The cathode is preferably heated sunlciently to ionize the vapor therein (above 1200 C. when using caesium vapor) by an auxiliary source of current connected thereto. By suitably connecting the auxiliary source, it may also serve to produce the aforesaid potential gradient along the mouth of the cathode. While the entire cathode may be heated as herein described, the heat is particularly effective in the region of the cathode opening and for many purposes other regions of the cathode may be at a lower temperature.

In a further aspect the invention involves the use of an electric field for directing the electronic discharge from the interior of the cathode through the mouth thereof to the anode, the field preferably being combined with a magnetic field extending longitudinally of the opening to restrain the electrons from impinging upon the walls of the cathode.

In a still further aspect the invention consists in using an alkali vapor, preferably caesium vapor, as the aforesaid gas in the hollow cathode. This gas is readily ionized by thermal means and the gas within the cathode becomes intensely ionized thereby greatly increasing its current carrying ability. The attendant radiation of this volume of highly ionized gas is also believed to be advantageous since it liberates electrons from neutral molecules and does so more or less independently of superposed electric or magnetic fields. During operation the caesium vapor,

which is readily ionizable gas, is present as a gaseous atmosphere in the tube at a substantial pressure" (for example, of the order of 10 microns) at which the requisite number of positive ions are supplied to the space discharge by gas ionization during operation to neutralize the space charge of the electron discharge current to the desired extent, secure a low cathode voltage drop, and sustain a gaseous discharge at low voltage drop between the cathode and anode.

The use of caesium vapor or the like is sharply distinguished from the use of a caesium coating on a cathode since the cathode preferably operates at a temperature higher than that at which such a coating can adhere. The liberation of electrons from the cathode results from the intensely ionized volume of vapor in the cathode together with thermionic emission in addition. Owing to the fact that the action of the vapor is substantially confined to the comparatively small volume in the cathode, where most of the vapor is trapped under relatively high pressure, the required quantity of alkali is very small.

In another aspect the invention also involves the reduction or elimination of the space charge in the region of the anode, thereby requiring only a very small potential difference between cathode and anode even when passing large current and minimizing the anode loss. This is preferably accomplished in major part by heating and thermally ionizing the gas in the region of the anode with heat generated independently of the electronic discharge, the electronic discharge having little eflect upon the ionization when the pressure outside the cathode is low as in the preferred embodiments. For certain uses, such as rectification, this thermal ionization also permits the current to be varied over a vast range without rendering the device inoperative. The thermal ionization in the region of the anode may be effected by the same source of heat that heats the cathode, as for example by enclosing the cathode and anode within a common heat shield. This thermal ionization is also facilitated by making the electron-receiving surface of the anode reentrant or cupped or otherwise partially enclosing the electron-receiving surface.

For the purpose of illustration embodiments of the invention are shown in the accompanying diagrammatic drawings, in which:

Figs. 1, 2 and 3 are longitudinal central sections of electronic devices with associated circuits;

Fig. 4 is a section on line 44 of Fig. 1:

Fig. 5 is a section on line H of Fig. 2;

Fig. 6 is a detailed section of a modification of a part of Fig. 2; and

Fig. '7 is an enlarged view of certain parts of Fig. 3.

Theparticuiar embodiment shown in Figs. 1 and 4 comprises an evacuated hermetically closed tube or vessel l containing a hollow thermionic cathode 2, an anode 3 and a heat shield 4. The tube I is preferably completely evacuated except for a small amount of caesium or other alkali. The alkali may be in solid or vaporous form, but ordinarily it is at least partly solid. 5 is an electro-magnetic coil surrounding the tube for the purpose of creating a magnetic field longitudinally of the tube. While the tube is adapted .to many uses, it isillustrated for use as a rectifler, receiving current through the transformer I and rectifying the current for a suitable load I.

and outer cylinders I and 8, the bottom of the inner cylinder being closed and the bottom of the outer cylinder being open at ll. The upper ends of the two cylinders are closed except for axial discharge openings, the peripheries of which are joined by a neck H. The diameter of the neck II is restricted and is preferably of the order of or less than the mean free path of the vapor molecules outside the cathode. Leads l2 and I! connect the lower ends of the inner and outer cylinders to the opposite sides of a source of potential I4 which serves to heat the cathode by virtue of the resistance of the walls of the cathode, and also serving to produce the aforesaid potential gradient along the neck H, the positive terminal of the source being connected to the outer cylinder and thence to the upper end of the neck I l, making the parts of said neck lying farther away from the anode more negative. The walls of the cathode thus constitute means independent of the discharge between the cathode and anode for heating the interior surfaces of the cathode, including the walls of neck II, to temperature of thermionic emission. Thus the walls of the neck constitute oppositely disposed extended juxtaposed areas spaced from each other by a distance of the order of the mean free path of the gas or less. Inasmuch as the cross-sectional area of the path of the current conducted through the cathode is least along the neck II, the heat will be more intense in this region. From the above it will be seen that the neck II can properly be termed a chamber, the walls of which are to be heated to temperature of thermionic electron emission during operation. I

The cathode may be formed of tungsten or other suitable material.

The anode 3 is also cylindrical, the upper end being closed and the lower end open. The diameter of the opening into the anode is preferably somewhat greater than the diameter of the opening in the neck of the cathode. The anode is also preferably placed in close juxtaposition to the cathode with its opening or mouth co-axial with the opening or mouth of the cathode.

The shield 4 constitutes an enclosure which is shaped closely to confine the cathode and anode to localize the heat developed in the cathode by the source l4. Shield 4 likewise prevents extension of the discharge from the space within it to the space bordering the walls of tube I. The shield may be mounted in any suitable manner, and as shown in Fig.4 it is mounted on the lead of the anode, in which case the lead should of course be relatively rigid. The inner surface of the shield is preferably bright to reflect the heat.

When the interior of the cathode 2 is heated (for example above 1200" C.), the vapor inside the cathode, and particularly in the region of the neck II, is highly ionized, and owing to the potential gradient maintained lengthwise along the neck I I the vapor is pumped into the cathode until a relatively high pressure is established therein. The theory of this pumping action is believed to be substantially as follows:

As a result of the continuous molecular movement of the vapor in the tube, neutral molecules (that is unionized molecules) wander into the neck of the'cathode where they are ionized by the intense heat in this region. These ions are thus trapped in the neck and impelled to the interior of the cathode by the potential gradient along the neck ll the upper end of the neck hav- 75 The tubular cathode 2 is in the form of inner ing positive polarity. This trapping action is 1| augmented by making the diameter of the neck V II less than the mean free path of the vapor n olecules outside the cathode because substanially all molecules tending to enter the cathode I collide with the wall of the neck and become ionized as a result of the high temperature of the wall, whereby substantially all neutral mole-- cules which are capable of escaping are converted into ions which may be trapped. The difference 10 in pressure between the interior and the exterior of the cathode may be regulated by varying the voltage of source 14. A higher internal pressure may also be produced by making the diameter of the neck ll smaller.

I With the cathode 2 full of highly ionized alkali vapor under substantial pressure, anelectronic discharge from the interior of the cathode through the neck II to the interior of the anode is readily produced by a relatively low potential U applied between the anode and cathode, reverse current being prevented upon reversal ofpotential because the space near the anode does not contain highly ionized vapor under pressure.

The space charge near the interior surface of U anode 3 is reduced or nullified by the positive ions generated as a result of the high temperature of the juxtaposed cathode, the two electrodes being together enclosed within the common shield. Thus the walls of the cathode carrying the heating current likewise constitute means independent of the discharge for heating and thermally ionizing the gas adjacent the electron re ceiving face of the anode. The vapor pressure inside the anode is preferably too low for appreciable ionization by collision so that the ion-' ization is not substantially affected by the electronic discharge. Thus the rectifying property of the tube is not a function of the load as in prior rectifiers of the gas or vapor type; consea quently heavy loads do not greatly reduce the voltage which the device will rectify properly.

The longitudinal magnetic field produced by coil 5 reacts upon the electronic stream, tending to direct it axially through the neck I I and tend- G ing to restrain the stream from contacting with the wall of the neck.

In the embodiment shown in Fig. 2, the cathode i 5 is in the form of a cylinder telescoped over the ends of leads i6 and having an opening H U on its upper side. Surrounding the cathode is a cylindrical shield it having a larger opening 19 coaxially with opening H. The anodes 20 and N are in the form of plates disposed in planes perpendicularly to the axis of the cathode and 55 arranged equal distances on opposite sides of the axis of openings I1 and IS. The cathode may be formed of tungsten or other suitable material.

The cathode i5 is heated, by virtue of the re- 80 sistance of the walls of the cathode, by current induced in secondary coil 2| by primary coil 22 and the anodes are connected to the opposite ends of the secondary of transformer 23.

' The midpoint of the secondary of transformer 23 is connected to the midpoint of the secondary 2! through a sustaining inductance Z4 and a suitable load 25. In this case the anodes 20 and 20' supply the positive potential near the mouth of the cathode which causes the vapor to be 70 pumped into the hollow cathode tube until a suitable pressure is built up therein. The electronic discharge issues from the interior of the hollow cathode and passes through openings l1 and I9, and thence passes alternately during succeeding 75 half cycles to the anodes 20 and 20' respectively,

plates or electrode projections at the sustaining coil 34 insuring a continuous relative negative polarity of IE.

In the modification shown in Fig. 6 the anodes .and 30', corresponding to 20 and 20' in Fig. 2, are in the form of rings concentric with the 5 cathode lli' (corresponding to I! in Fig. 2) and disposed on opposite sides of the cathode opening H. In this modification the shield I8 is v dispensed with inasmuch as the anodes 30 and 30' may be constructed to function also as heat 1 The tube shown in Figs. 3 and 7 comprises a cylindrical thermionic cathode structure 3| come prising a hollow conducting member telescoped over a leading-in support 32 having at its 1' upper end a flange 33 which is connected at its periphery to another leading-in conductor II. The anode is in the form of a wire or rod 35 pro- Jecting toward the mouth of the cathode; By connecting the leads 32 and 34 to the negative 59 and positive ends respectively of a suitable source of potential 36 the cathode may be intensely heated and the mouth of the cathode maintained at a higher positive potential than the lower end. Thus the aforesaid potential gradient is produced throughout the length of the cathode. In this 7 way vapor is pumped into the hollow cathode as above described. In this embodiment likewise the walls of the hollow conducting member of the cathode constitute means independent of the discharge between the cathode and anode for electrically heating the electron-emitting area of the cathode to temperature of thermionic electron emission. The heat localizing screen is preferably omitted in this construction so that 35 more current can be supplied to the cathode by the source 36 without over-heating the cathode, thereby creating a larger potential gradient than would be possible with the source 36 of lower potential. A high potential gradient may be obd0 tained without over-heating the cathode by forming the cathode of boronor carbon or other refractory material of high electrical resistance. A, magnetic field, such as described in Fig. 1, may also be used in Fig. 3. 6B

The cathode has a plurality of perforated extending transversely across its hollow interior near its mouth. These plates El are spaced longitudinally of the cathode. The plates ti constitute oppositely-disposed conducting wall members with relatively extended, juxtaposed surfaces bounding narrow spaces therebetween. These surfaces are heated to thermionic emission during operation by the current passing through the walls of the hollow conducting member of the cathode. The surfaces of the plates 6! thus constitute in conjunction with the interior surfaces of the hollow conducting member of the cathode an extended electron-emitting electrode area. The perforations in said plates serve as discharge openings for passing a space discharge between said electron-emitting area and the anode 35. Likewise the hollow conducting member of the cathode constitutes an enclosure or chamber surrounding said plates for maintaining the surfaces of the plates at temperature of electron emission during operation and simultaneously maintaining the caesium vapor between said surfaces at high temperature and excited condition at which a discharge at low voltage drop is secured between the cathode 3i and the anode 35. The anode in this and other modifications is p0- sitioned relatively to the cathode to maintain during operation a temperature insufiicient to produce copious electron emission from said anode. Since electron emission occurs from the interior walls of the cathode and since the heat radiation occurs from the exterior walls of the cathode, it will be seen that the electron-emitting surface is different from the outer heat-radiating surface. It will also be seen that the plates H, which are heated to thermionic emission during operation, partition ofi narrow intercommunicating spaces or cells within the hollow cathode interior. The perforations in said plates form common discharge spaces into which all of the said narrow spaces terminate or open and through which a discharge may be maintained between the anode and the surfaces of said plates.

In the embodiment in which the cathode has a reduced neck or outlet opening (as in Fig. 1), and in which a magnetic field is produced longitudinally of the discharge opening, further pumping action is produced by the interaction between the magnetic field and the field produced by the electronic discharge, this interaction causing the vapor to whirl about the axis of the discharge opening, and thereby pumping gas into the cathode by centrifugal action as described and claimed in my co-pending application Serial No. 55,262 filed September 9, 1925.

In the embodiment in which the cathode has a reduced neck or outlet opening (as Fig. 1), and in which a magnetic field is produced longitudinally of the'discharge opening, further pumping action is produced by interaction between the magnetic field and the field produced by the electronic discharge, this interaction causing the vapor to whirl about the axis of the discharge opening,

and thereby pumping gas into the cathode by centrifugal action as described in my copending merits and that many other modifications and adaptations may be made within the scope of the appended claims. For example, by making the interior and exterior surfaces of the cathode highly reflecting, as by polishing the surface, less heat escapes from the interior of the cathode through the walls thereof and a higher temperature can be maintained inside the cathode, thereby augmenting the ionization.

I claim:

I. An electrical space discharge device comprising a vessel having therein an anode, a thermionic cathode comprising a hollow conducting member having in the interior a plurality of elements, the surfaces of said elements constituting in conjunction with the interior surfaces of said hollow member an extended electronemitting area, means independent of the discharge for heating said electron-emitting area to thermionic emission, said cathode having a discharge opening for passing a space discharge between said electron-emitting area and said anode, and an ionizable gas in said vessel at substantial pressure at which sufiiclent positive ions are supplied to the space discharge during operation to neutralize the space charge and secure low cathode voltage drop.

2. An electrical space discharge device comprising a hermetically closed vessel containing an anode, and a thermionic cathode structure having a plurality of oppositely-disposed conducting wall members with relatively extended, juxtaposed electron-emitting surfaces bounding narrow spaces therebetween designed to be heated to thermionic emission during operation, an ionizable gas having during operation a pressure sufilcient to sustain a discharge at low voltage drop between anode and cathode, means independent of the discharge for electrically heating said electron-emitting surfaces to a temperature of electron emission, said cathode structure also comprising a hollow enclosure member surrounding said wall members for maintaining said electron-emitting surfaces at temperature of electron emission during operation of the device and simultaneously maintaining the gas between said surfaces at high temperature and excited condition at which a discharge at low voltage drop is secured between said cathode and anode.

3. An electrical space discharge device comprising a vessel containing an anode, a cathode structure constituting an enclosure, said cathode structure having in the interior of the enclosure oppositely-disposed conducting wall members having juxtaposed electron-emitting surfaces to be heated to thermionic emission during operation and partitioning oif cells from the interior space of said enclosure, an ionizable gas having during operation a pressure at which a discharge at low cathode voltage drop takes place between said anode and said enclosure, and means independent of the discharge for electrically heating said electron-emitting surfaces to a temperature of electron emission.

4. An electrical space discharge device comprising a vessel containing a cathode structure constituting an enclosure and having a series of conducting electrode projections extending transversely across said enclosure and subdividing the same into a plurality of relatively narrow cells opening into a common discharge space within Y said enclosure, means independent of the discharge for heating said projections to thermionic emission during operation, an anode for maintaining through'said common discharge space a discharge with the surfaces of said projections, and a gas filling at a pressure suflicient to sustain a discharge by gas ionization between said electrodes.

5. A unidirectional gaseous discharge tube comprising a vessel containing a gaseous atmosphere to be ionized to maintain a discharge, a cathode constituting a hollow chamber with an interior electrode surface in said vessel, the interior of said cathode chamber having an electrode surface formed of a plurality of closely spaced projecting wall portions constituting a plurality of intercommunicating cells terminating into a common space within said hollow chamber, means independent of the discharge for heating said wall portions to thermionic emission during operation, and an anode disposed outside said cells to maintain a discharge through said atmosphere with the interior conducting surfaces of said cathode through said common space.

6. A gaseous discharge device comprising an anode, a hollow cathode containing alkali vapor and having a discharge opening therein, the said opening having a diameter of the order of the mean free path of the gas molecules outside the opening, and means for ionizing the vapor inside the cathode independently of the electronic discharge.

'7. A gaseous discharge device comprising an anode, a hollow cathode containing alkali vapor and having a discharge opening therein, the said opening having a diameter of the order of the mean free path of the gas molecules outside the opening, and means for heating the vapor inside the cathode independently of the electronic discharge.

8. A gaseous discharge device comprising a 5 tube containing alkali vapor, an anode, a hollow low thermionic cathode constituting a chamberhaving an interior electron-emitting surface, said chamber having at one end a space discharge opening, an ionizable gas having during operation a pressure suflicient to supply the requisite number of ions necessary to neutralize the space charge of the discharge between said cathode and anode, and means for conducting current to heat said electron-emitting surfaces to tempe ture of electron emission during operation of the device and to simultaneously maintain the gas in said vessel in a state of ionization at which low cathode voltage drop is secured, said means including means for maintaining lengthwise of the interior walls adjacent to said discharge opening a potential gradient at which the parts lying farther away from the anode will be more negative.

10. An electrical space discharge device comprising a vessel having therein an anode, a hollow thermionic cathode constituting a chamber having an interior electron-emitting surface, said I chamber having at one end a space discharge opening, an ionizable gas having during operation a pressure sumcient to supply the requisite number of ions necessary to neutralize the space charge of the discharge between said cathode and D; anode, and means for conducting current to heat said electron-emitting surfaces to temperature of electron emission during operation of the device and to simultaneously maintain the gas in said vessel in a state of ionization at which low cath- B ode voltage drop is secured, said means including means for maintaining lengthwise of the interior walls adjacent to said discharge opening a potential gradient at which the parts lying farther away from the anodewill be more negative.

W 11. An electrical space discharge device comprising a vessel having therein an anode and a hollow thermionic cathode having an extended interior solid electron-emitting wall surface, said cathode having a discharge opening, and an ion- 5 izable gas in said vessel at a pressure suiiicient to su ply the requisite number of ions necessary to neutralize the space charge of the discharge between said cathode and anode, and means for maintaining lengthwise of said discharge opening a a potential gradient.

12. An electrical space discharge device comprising a vessel having therein an anode, a hollow thermionic cathode comprising a chamber having an interior electron-emitting surface, said chamher having at one end a space discharge opening for passing a discharge to said anode, an ionizable gas in said vessel, and means for producing a magnetic field axially along said tubular cathode chamber, the width of said opening being of the order of the mean free path of the gas in said vessel.

13. An electrical space discharge device comprising a vessel having therein an anode, a hollow thermionic cathode comprising a chamber having i an interior electron-emitting surface, said chamher having at one end a space-discharge opening for passing a discharge to said anode, alkali metal vapor in said vessel, and means for producing a magnetic field axially along said tubular cathode chamber, the width of said opening being of the order of the mean free path of the gas in said vessel.

14. A gaseous discharge device comprising a tube containing gas, an anode and a hollow cathode having therein a discharge opening having a diameter of the order of the mean free path of gas molecules outside the opening, and means for maintaining the gas pressure inside the hollow cathode higher than outside the cathode.

15. A gaseous discharge device comprising spaced electrodes for passing a discharge, one of the electrodes being a hollow cathode and containing gas and having a restricted opening therein, means for ionizing the gas independently of said discharge, the hollow cathode having a highly reflective interior surface thereby to augment the ionization, the said hollow cathode having a discharge opening therein, the said opening having a diameter of the order of the mean free path of gas molecules outside the opening.

16. A gas-filled discharge tube comprising an anode, a hollow cathode having a discharge opening formed by a neck portion having a diameter of the order of the mean free-path of the molecules outside the hollow cathode, and means for ionizing the gas in the said hollow cathode independently of the discharge.

17. An electrical space discharge device comprising a vessel having therein an anode and a hollow cathode constituting an enclosure around a part of the space in said vessel and having an extended interior solid electron-emitting wall surface having means for heating said surface to temperature of thermionic emission during operation, said cathode having a discharge opening for passing a space discharge between the interior emitting surface thereof and said anode, and an ionizable gas in said vessel at substantial pressure at which suflicient positive ions are supplied to the space discharge during operation to neutralize the space charge and secure low cathode voltage drop, said cathode discharge opening having a width of the order of the mean free path of the gas in said vessel.

18. An electrical space discharge device comprising a vessel having therein an anode, a thermionic cathode having oppositely-disposed wall members with relatively extended juxtaposed thermionic emitting areas bounding a narrow space therebetween, heater means for heating said emitting areas to temperature of thermionic emission during operation, an ionizable gas inert with respect to said electrodes in said vessel at a pressure sufficient to supply during operation the requisite number of ions necessary to neutralize the space charge of the electron current between said cathode and anode, said juxtaposed thermionic emitting areas being spaced from each other by a distance of the order of the mean free path of the gas in said vessel.

19. An electrical space discharge device comprising a vessel having therein an anode, a hollow cathode constituting an enclosure around a part of the space in said vessel and having an extended interior surface, said cathode having a discharge opening for passing a space discharge between said surface and said anode, and means for heating said surface to temperature of thermionic emission during operation of the device and simultaneously maintaining an ionizable gas in said enclosure ionized at substantial pressure greater than outside the enclosure at which sumcient positive ions are supplied to the space discharge to neutralize the space charge and secure low cathode voltage drop, said discharge opening having a width of the order of the mean free path of the gas in said vessel outside said enclosure.

20. A gaseous discharge device comprising a tube containing gas, a cathode and anode, and means independent of the discharge for ionizing the gas adjacent the electron receiving face of the anode to reduce the space charge near the anode, the said cathode having a discharge opening therein, the said opening having a diameter of the order of the mean free path of gas molecules outside the opening.

21. A gaseous discharge device comprising a tube containing gas, a cathode and anode, and means for heating the gas adjacent the electron receiving face of the anode independently of the discharge, to reduce the space charge near the anode by thermal ionization, the said cathode having a discharge opening therein.

22. A gaseous discharge device comprising a tube containing gas, a cathode, an electrode having an electron receiving surface, and means for heating the gas adjacent said surface, the said cathode having a discharge opening therein, the

said opening having a diameter of the order of the mean free path of gas molecules outside the openns.

23. A gaseous conduction device comprising a container having a gas therein, an anode and cathode in spaced relation to each other, said cathode comprising a hollow chamber having an electron-emitting inner surface, said cathode being designed to operate in the presence of substantial ionization during normal operation,'and means for heating said cathode, the said cathode having an opening, the diameter of which is of the order of the mean free path of gas molecules outside the opening.

24. A gas-filled discharge device comprising spaced electrodes adapted to have a discharge pass between them, both of said electrodes being hollow and containing gas, and means for ionising the gas in said hollow electrodes independently of said discharge, said electrodes having opposed mouths through which the discharge from the interior of one electrode to the interior of the other electrode, the mouth of one electrode having a diameter of the order of .the mean free path of the gas molecules outside the mouth.

25. An electrical space discharge device comprising a vessel having therein an anode and a in said vessel at a pressure sumcient to supply during operation the requisite number of ions necessary to neutralize the space charge of the electron current between said cathode and anode, and a shield constituting an enclosure around said anode and cathode for preventing extension of the discharge from the space within said enclosure to the space bordering the walls of said vessel.

26. An electrical space discharge device comprising a vessel having therein an anode, a hollow cathode constituting an enclosure around a part of the space in said vessel and having an extended interior surface, said anode being designed and positioned relatively to said cathode to maintain during operation a temperature insufficient to produce copious electron emission therefrom, said cathode having a discharge opening for passing a space discharge between said surface and said anode, and means for heating said surface to thermionic emission during operation of the device and simultaneously maintaining an ionizable gas in said enclosure ionized at substantial pressure greater than outside the enclosure at which sufficient positive ions are supplied to the space discharge to neutralize the space charge and secure low cathode voltage drop.

27. A gaseous discharge device comprising a tube containing alkali vapor, an anode, a hollow cathode having a discharge opening, said opening having a diameter of the order of the mean free path of the gas molecules outside the opening, and means capable of maintaining the alkali vapor within the cathode at a higher DIG? sure than outside thereof independently of the electronic discharge. I

28. A gaseous discharge device comprising a tubecontaining alkali vapor, an anode, a hollow cathode having a discharge opening, said opening having a diameter of the order of the mean free path of the gas molecules outside the opening, and means operating, whether or not the electronic discharge is present, for maintaining the alkali vapor within the cathode at a higher pressure than outside thereof.

29. An electrical space discharge device comprising a vessel having therein an anode, a thermionic cathode comprising conducting members surrounding a plurality of spaces bordered by a relatively large surface area, means, independent of the discharge, for heating said surface area to thermionic emission, and an ionizsble gas in said vessel at substantial pressure at which sufflcient positive ions-are supplied during operation to the space discharge to neutralize the fice charge and secure low cathode voltage CHARL'BCLBHITH. 

